if (typeof window.event != 'undefined')
	document.onkeydown = function(){ 
		if (116==event.keyCode){
			event.keyCode = 27;
			return false; 
		}
	}
else
	document.onkeypress = function(e){		
		if (116==e.keyCode){
			return (e.keyCode != 116); 
		}
	}